Not everyone is unhappy about the desperate straits of the Greek economy. A group of financial "investors" made a killing on Greek debt on Tuesday – purely by being the most unscrupulous players in the market.

Dart Management is an investment fund based in the Cayman Islands, a British territory notorious for its tax haven status. Dart's business model has earned it the title "vulture fund".

Vultures "invest" in the sovereign debt of countries facing crisis – meaning they can buy debt cheap. They then "hold out" against any form of write-down on this debt. By doing this, they hope to get paid out in full. Given they paid a fraction of the value of the debt, getting full repayment represents an enormous profit.

Vulture funds honed their skills against developing countries: Elliott Associates, a US hedge fund, pioneered the model back in the 1990s, winning a case against Peru which earned it 400% what it paid for the debts. Elliott is also believed to own some of Greece's debt. Dart meanwhile took $600m from Brazil following its 1993 crisis.

In recent years, vulture funds have targeted some of the world's most impoverished countries. Liberia and Zambia have both been hauled before British courts and told to pay out to funds which have bought up very old debts, run up by dictatorial regimes, very cheaply.

When countries refuse to pay up, the vultures chase them around the world, attempting to seize the overseas assets of the country in question. In one case, a particularly noxious vulture fund tried to seize aid money headed for the Republic of Congo. To this day, Democratic Republic of Congo is being pursued by another fund called FG Hemisphere and is currently in legal dispute over assets based on Jersey. The final appeal will be heard in London on 28 May, but under Jersey law.

A law passed in the dying days of the last parliament now prevents vulture funds profiteering on the old debts of very low income countries in British courts – a huge step forward. But this law does not apply to other countries – from Nigeria to Greece – or to new debts.

Argentina gives some clue of what may be in store for Greece in years to come. Since that country defaulted back in 2001, after years of unjust debt burdens brought it to its knees, it was swamped with lawsuits from vulture funds that refused to accept Argentina's writedown. These funds include both Dart and Elliott, and an umbrella group known as the American Task Force Argentina which has attempted to capture US foreign policy as a means of forcing Argentina to pay up on these debts.

For such companies, a crisis as big as Greece's is mouth-watering. For months vulture funds have been working out the best way to pursue vulture strategies against Greece. Vultures have been buying up foreign-law Greek bonds because bonds controlled by Greek law were forced by a majority to accept the writedown.

The Greek writedown was a very good deal for bondholders who were paid 50% of the face value at a time when those same bonds were actually trading for around 35% value – and they got a cash incentive. But that was not good enough for the vultures. American law firm Bingham McCutchen was reported to be trying to organise a group of such funds in order to take legal action to get paid the full value of their bonds.

For some of those funds, Tuesday was payday. Rather than risk legal action, Greece decided to make a repayment of €436m on its foreign-governed debts. Of this total, 90% reportedly went to Dart Management. While the Greek welfare state collapses and society suffers rises in rates of suicide, murder and HIV, Kenneth Dart can sit back on his 220ft yacht in the Cayman Islands and count his winnings.

Holders of over €6bn refused to swap Greek debt – so this will not be the end of such scandals. But we are not powerless to stop them. One vulture fund chief told the Financial Times: "We thrive on people being misinformed." Step one is to introduce transparency into bond trading. It is shocking that the people of Greece do not even know who owns their debt, when they bought it or how much they paid for it.

David Cameron and George Osborne have been clear that the EU needs to sort out its problems – but they have done nothing to stop the vulture funds whose debt is governed by British law. The government can force all British-law creditors to accept the writedown already agreed. Or it could go further and legislate to prevent exorbitant gains being made on debts purchased on the secondary market – such a law has already been floated in the US Congress.

Greece is in the frontline of a battle between unscrupulous investors and people who want their economy to work in the public interest. It is not good enough for governments to simply sit back and declare "that's just how things are".